Introduction: Coronal plane Fractures of the femoral condyle are known as Hoffa fractures. Although isolated posterior Hoffa fractures of medial femoral condyle have been rarely reported, no reports are available regarding the anterior fracture of this type. Here, we report a large isolated anterior osteoarticular fracture of the medial femoral condyle. Case Presentation: A 16-year-old girl with a traumatic open joint injury of the right knee caused by a car-to-pedestrian accident was referred to our emergency department for further evaluation. A physical examination of the knee revealed effusion and limited knee range of motion. While no obvious fracture was detectable on plain radiographs of the knee, a large anterior osteoarticular fracture of the medial femoral condyle was observed in computed tomography (CT), which was detached from the medial condyle. The fracture was managed with open reduction and internal fixation. Eight weeks after the surgery, the patient retrieved the full knee motions and the complete union of the fracture was observed. No complication was reported by the patient at a follow-up period of 12 months. Conclusions: In cases with knee tenderness and/or effusion and normal plain radiographs, whenever there is a discrepancy between plain radiographs and clinical symptoms of the patient, a further evaluation of the knee with a CT scan and/or MRI is necessary to avoid missing a Hoffa fracture, which could be successfully treated if timely diagnosed.